Collaborative Research: Fundamental Properties of Local Subdwarfs

AST 0205789 Terndrup关于银河系的形成和演化的许多悬而未决的问题需要改进的知识，在银河系的晕和厚盘中的局部贫金属亚矮星的运动学和化学富集模式，以及如何将这些与球状星团恒星进行比较。即使经过几个世纪的时间，目前的样品仍然不能充分覆盖球状星团中所看到的金属丰度和运动学的范围，而对本地贫金属巨星的观测则提供了诱人的证据，证明本地晕星与具有相同金属丰度的球状星团中的晕星之间存在着显著的差异。在最近的贫金属恒星巡天中发现的大约150颗次矮星的严格挑选的样本和组成。也将有新的理论努力，探索主序星光度对详细的恒星化学成分和经常被忽视的物理，如氦扩散和旋转的依赖。该项目还将产生关于晕和厚盘贫金属尾部的运动学和星星形成历史的宝贵信息，确定在丰度模式和运动学上与球状星团恒星完全匹配的次矮星样本，并改进球状星团主序列的温度和丰度标度，以便与巨型分支的光谱测定进行比较。还将对球状星团的相对和绝对年龄进行系统研究，重点是减少理论平面上的误差。重要的是，该项目将使社区能够充分利用未来的FAME和SIM卫星任务，这将测量样品中次矮星的精确视差，从而产生主矮星的绝对校准。球状星团的序列光度和它们的距离。目前的距离估计只有10 - 15%，导致年龄误差约30%，不足以可靠地探索球状星团系统中的年龄分布，甚至与恒星演化理论的预测相比，设定宇宙年龄的下限。

AST 0205789TerndrupMany outstanding issues concerning the formation and evolution of the Milky Way require improvedknowledge of the kinematics and chemical enrichment patterns of local metal-poor subdwarfs in theGalaxy's halo and thick disk, and how these compare to globular cluster stars. Even after several recentefforts, current samples do not adequately cover the range of metallicities and kinematics seen in globularclusters, while observations of local metal-poor giants give tantalizing evidence of significant differencesbetween local halo stars and those in globular clusters of the same metallicity.This project will improve the observational situation by obtaining accurate and self-consistentmeasures of temperature, reddening, and composition for a critically selected sample of approximately150 subdwarfs identified in recent surveys for metal-poor stars. There will also be new theoretical effortsto explore the dependence of the main-sequence luminosity on detailed stellar chemical composition andon often-neglected physics such as helium diffusion and rotation. This project will also yield valuableinformation on the kinematics and star formation history of the halo and the metal-poor tail of the thickdisk, identify samples of subdwarfs that are well matched in abundance patterns and kinematics toglobular cluster stars, and improve the temperature and abundance scales of globular cluster mainsequences for comparison to spectroscopic determinations on the giant branch. There will also be asystematic study of the relative and absolute ages of globular clusters, with a focus on reducing the errorsin the theoretical plane.Importantly, this project will enable the community to take full advantage of the future FAME andSIM satellite missions, which will measure accurate parallaxes for the subdwarfs in the sample andthereby yield the absolute calibration of the main-sequence luminosity for globular clusters and hencetheir distances. Current distance estimates are only good to 10 - 15%, resulting in age errors of about30%, insufficient to reliably explore the age spread in the globular cluster system or even set lower limitsto the age of the Universe by comparison with the predictions of stellar evolution theory.